Electric current converting system



Dec. 25, 1945. .1. G. LINN 2,391,787

'ELECTRIC CURRENT CONVERTING SYSTEM Filed Dec. 8, 1945 5 Sheets-Sheet l mmw Dec. 25, 1945. J. G.- LINN 2,391,787

ELECTRIC CURRENT CONVERTING SYSTEM Filed Dec. 8, 1945 s Sheets-Sheet 2 Dec. 25, 1945. J. G. LINN 2,391,787

ELECTRIC CURRENT CONVERTINGv SYSTEM Filed Dec. 8, 1943 5 Sheets-Sheet 3 Patented Dec. 25, 1945 ELEc'mIc cunass'r comamc SYSTEM James G. Linn, West Allis, Wis, asslgnor to Allis.

Chalmers Manufacturing Company, Milwau- I kee, Wis., a corporation of Delaware Application December 8, 1943, Serial No. 513,436

(Cl. TIL-312) 9 Claims- This invention relates in general to improvements in electric current converting systems and more particularly to means for regulating theflow of current through a dynamoeiectric machine and an electric valve converting system connected to a common supply or load circuit.

Current converting systems of the electric valve type are frequently connected with supply circuits therefor to operate in parallel with dynamoelec-= tric machines functioning as motors, or are connected with'load circuits therefor to operate in parallel with dynamoelectric machines functioning as generators. It is not generally feasible, however, to impart to a converter and to a dynamoelectric machine associated therewith such inherent voltampere characteristics as would result in the desired current distribution therebetween. Means are therefore generally provided for controlling the conductivity of the valves oi the converter in such manner as to obtain the desired characteristics for the system.

The regulators generally utilized for this purpose however require a substantial time to complete their response to a change in an operating condition of the system to be regulated, and serious disturbances may take place during this time of response. For example, if an alternating current rectifying system is connected in parallel with a substantially flat compounded direct cur rent generator a sudden decrease in the load will cause the output voltage of the converter to rise above the terminal voltage of the generator a substantial extent before the regulator returns it to its desired value. The rise in the converter voltage may be suflicient to cause the converter to supply current to the generator which then operates as a motor, thereby causing operation of the usual protective devices associated therewith to place the converter and the generator out of operation.

Such disturbances are avoided by causing the flow of current through the converter to modify the characteristic of the dynamoelectrlc machine. In a preferred embodiment of the invention a dynamoelectric machine provided with an armature winding and a series field winding is associated with a converter efiectlvely connected in parallel with the armature winding to thereby modify the action of the field winding. A shunt having predetermined inductance may be connected in parallel with the series field winding to further modify the action of the field winding or to limit the modifying effect of the converter thereon to periods of transient operation of the system.

The converter may be provided with a regulator imparting thereto a predetermined chameteristic. The regulator may also cause a predetermined distribution of current between the converter and the dynamoelectric machine, thereby modifying in eflect the characteristic of the converter in dependence upon the characteristic of the machine.

It is therefore an object of the present invention to provide an electric current converting system in which the characteristic of a dynamoelectric machine is modified by a static converter associated therewith.

Another object of the present invention is to provide an electric current converting system in which current distribution between a static converter and a dynamoelectric machine is controlled by an electromechanical regulator during steady state operation and is controlled by static means during transients.

Another object or the present invention is to provide an electric current converting system in which the characteristic of a dynamcelectric machine is different during steady state operation and during transients.

Another object of the present invention is to provide an improved electric current converting system in which the characteristic of a static converter is modified by a dynamoelectric machine operating in parallel therewith.

Objects and advantages other than those above set forth will be apparent from the following description when read in connection with the accompanying drawings, in which:

Fig. l diagrammatically illustrates one embodiment of the invention in which the series field of a compound direct current generator is partially controlled by the current of a static converter provided with an electromechanical regulator imparting thereto a predetermined characteristic;

Fig. 2 is a diagram oi the operating characteristics of the dynamoelectric machine and of the static converter illustrated in Fig. 1;

Fig. 3ldiagrammaticaily illustrates a modified embodiment of the present invention in which the regulator is partially controlled by the current of the dynamoelectric machine, and

Fig 4 diagrammatically illustrates a further modified embodiment of the present invention differing from the embodiment illustrated in Fig. 3 in the manner-of connecting the regulator to the circuits of the system.

Referring more particularly to Fig. 1 of the drawings by characters or reference, a dynamoelectric machine 8 is provided with an armature I, a series field winding 6 and another field winding 9 excited from a suitable source, such as a battery ll, through an adjusting rheostat i2. Machine 6 may be a generator or a motor but it will be assumed that it operates as a generator to supply current to a direct current circuit is across which armature i and field winding 8 are serially connected. Generator 8 is driven by any suitable means such as a synchronous motor I l receiving current from a suitable alternating current circuit l8.

A static converter I '7 of the electric valve type is effectively connected in parallel with armature i and is connected with a suitable alternating current circuit It for the-conversion of current between circuits l8 and i3. Circuits l6 and i8 may be interconnected but t oube-free operation of the system is more difiicult to secure when the circuits are separate as the voltages of the two circuits may then vary relatively to each other both in magnitude and in frequency.

When machine 6 operates as a generator, converter IT is so arranged as to rectify current supplied thereto from circuit l8 and to supply the rectified current to c rcuit I 3 through winding 8 to thereby modify the characteristic of generator 6. Winding 8 may be bridged by an adjustable shunt l9 which may be rendered inductive by means of an adiustable reactor 2! serially connected therewith. to further modify the effect of the current of converter H on the operat on of winding 8 or to limit such effect to periods of transient operation of the system.

Converter i? may be of any suitable known type and may comprise a transformer 22 and a plurality of electric valves 23. Transformer 22 comprises a primary w nding 26 connected with the conductors of circuit is and a secondary winding 26 divided into a plurality of phase portions severally connected with the anodes 2? of the different valves. The valves may be prov ded with separate cathodes or the cathodes may be combined into a s ngle cathode structure 28 connected with one of the terminals of armature 7. Winding 28 is preferably arran ed to define a plurality of neutral points severally connected with the other terminal of armature i through an interphase transformer 29. Su table known means f not shown) are provided for rendering the oath-* ode emissive and for maintaining it in electron emissing condit on as is well known.

The conductivity of valves 23 may be controlled by any suitable means such as control electrodes SI of the rid type severally associated with anodes I 3. Each control electrode is connected with cathode 28 through acontrol circuit comprising a current limiting resistor 32 and one of the secondary phase portions oi a control transformer 33. The primary winding 3% of transformer 38 is ener ized from circuit l8 and the secondary winding 35 thereof is connected in star to provide a 'neutral point connected with the movable tap or sector 36 of a regulator 9'7. Sector 36 is associated with a resistor 38 to form a rheostat connected with any suitable source of current such as armature 1 through adjusting rheostats 39, 6|. Sector 36 is actuated by an electromagnetic mechanism a ainst the action of a spring 42 preferably so dimensioned as to oppose a substantially constant tordue to the movement of the sector re ardless of the position thereof.

The re ulator actuating mechanism comprises a field winding 43 connected across circuit is through the armature winding 65 of the regulator and throu h an adjusting rheostat 4B. A second field winding 47 is energized from a shunt 88 insorted in one of the connections of converter IV with armature l. The current through winding 67 may be adjusted by means of a shunt rheostat 69. As a result of the inertia of the movable elements of the regulator the latter operates with a substantial time of response in dependence upon sudden variations in the flow of current through circuit l3.

In operation, circuit l8 being energized, transformer 38 impresses on the different control electrodes 3| alternating potentials which render the different valves 23 intermittently conductive in sequence. Winding 26 impresses on Valves 23 voltages which bring anodes 27 sequentially to positive potentials with respect to the potential of cathode 28 to transmit current sequentially from winding 26 to suitable current consuming devices, such as electric motors (not shown), through shunt t8, winding 8 in parallel with shunt l9 and reactor 2| and through circuit it. Each valve however becomes efiective only when its control electrode has a potential which is more positive than the potential of cathode 28. The flow of current is returned from circuit it to winding 26 through interphase transformer 29.

Once circuit i3 is energized a current flows through resistor 38 and rheostats 39, il. The

voltage drop through rheostat 6i and through the portion of resistor 38 below the contact point of sector 36 is added to the voltage of winding 35. This voltage drop constitutes a negative potential component impressed on control electrodes 3i which retards the moments of positive energize.- tion thereof from winding 35 and thereby causes the output voltage of'the converter to decrease as is well known. If the neutral point of winding 35 were connected directly with cathode 2B the flow of current through the valves would take Place through the different valves at the maximum possible voltage. The voltage impressed on circuit it from converter i? would however decrease with increasing load and the converter would have a relatively steeply drooping volt am pere characteristic such as characteristic iii in Fig. 2.

The interaction of windings 68, 36 of regulator 37 tends to cause displacement of sector 38 in such a manner as to cause the output voltage of com verter ii to be lowered to a substantially constant value determined by the characteristic of spring t2 and thereby impart to the converter a fiat characteristic 52. This action is modified by winding 67 which is preferably so adjusted by rheostat d9 as to cause the characteristic of the converter to droop slightly as shown at 53. If it is desired that converter i1 and generator 6 deliver equal currents, characteristic 53 is chosen identical to that of generator Boperating alone. Characteristic 53 is a static characteristic based on the assumption that the flow of current through converter I! does not vary or varies so slowly as to enable regulator 37 to regulate the voltage ofthe converter without noticeable time lag.

Circuit I8 is also assumed to be energized so that motor It drives armature l at constant speed to generate current to be supplied to the current consuming devices through winding 8 in parallel with shunt l9 and reactor 21. It will first be assumed that the shunt path around winding 8 has a resistance substantially equal to that of winding 8 and a ratio of inductance to resistance also substantially equal to that of winding 8. The currents through winding 8 and through shunt l9 will therefore be equal during steady state operation. These currents will also vary at the that of armature l.

same rate during transients and therefore will remain equal. n

It winding 8 were short circuited generator 4 would have a steeply drooping characteristic such as characteristic 54 in Fig. 2. If the generator operated alone with winding 8 receiving the full current'oi armature 1 the generator would have characteristic IS, the difference between the ordinates of characteristics 53 and 54 being the voltage induced in armature I by the flow of its own current through'winding 8. In the system of Fig. I adjusted as assumed hereinabove, winding -8 always carries one-half of the load current.

Duringsteady state'operation, if armature I at any time carried less than one-half oi! the load current, its voltage would rise above characteristic 53 and the armature current would increase. Conversely, if armature 1 carried more than onehalf of th load current .its voltage would drop generator 8 and of converter 11 be represented at a predetermined instant by abscissa A. The.

generator and the converter then both operate at point B of characteristic 53. Abscissa 0A also represents one-half of the load current. Assume that the value or the half load current suddenly decreases to a value 00. Until regulator 31 changes its position, converter i! will operate along a line 55 parallel to line 51 and intersecting characteristic 53 at point B.

As abscissa 00 represents the new average of the converter current and of the generator current, the generator operating point must be on a line 58 symmetrical of line 56 with respect to line 51 of abscissa 00. If the converter and the generator were connected in parallel across -.circ uit it the generator would continue to operate with characteristic 53 as the current of winding 8 would remain the same as the generator would then be point D at the intersection of lines Eli and 58;. This shows that the generator. would be motoring while the converter would supply current to both the generator and the load. The operating point of the converter would be point 'E having the same ordinate as point D.

With the connections of Fig. 1 however, the effect of winding 8 is proportional not to the current of armature i but to the average load current. When the average load current has the value 00 the operating point of generator t must be on a line 58 parallel to line 54 and higher than line 54 by the voltage FG induced by the flow of current 00 through winding 8. The operating point of the generator is then point H at the intersection of lines 56 and 58 and the operating point of the converter is point K on line 55 at the same ordinate as point H. The current distribution between the generator and the converter is thus substantially improved until regulator ll causes both the generator and the converter to assume operating point G of abscissa QC on characteristic 53. The transient characteristic of the enerator for all variations of load current from value 0A may be obtained by joining points Hand B. This characteristic is closer to the transient characteristic 55 of the converter than characteristic The new operating point of v from that of winding 0 to cause generator I to carry a current equal to the converter current when the converter steady state characteristic is diil'erent from characteristic. 53. The inductance of reactor It may also be varied to vary the transient characteristics of the generator. The resistance and inductance of the shunt circuit may also be further modified to cause the converter and the generator to carry currents of diflerent values.

In the embodiment illustrated in Fig. 3 generator 6 is assumed to be disconnectable from circuit It by means of switches 8i 82,- 83 when converter i1 isto operate alone. Regulator 31 is provided with an additional field winding 64 connected across shunt l9 and reactor 2|. Windings 47 and B4 are wound on the core of the regulator with opposite polarity and may be disconnected by means of a switch when the converter is to operate alone. In the present embodiment winding 43 is made much weaker than windings 47 and 84 and spring 42 is weakened to a corresponding extent. When switches 8i 82, B3 and 65 are open and converter i'i supplies the entire load current to circuit l3, regulator 31 causes the converter to deliver current at a substantially constant voltage of value determined by the adjustment of rheostat 4B. I

When the switches are closed the converter cooperates with generator 6 and winding 4! receives a current proportional to the converter current while winding 84 receives a current proportional to the total load current. The number 01 turns of the two windings must therefore generally be different, winding ti having twice the number of turns of winding 64 if the converter and the generator are to carry equal currents and the reslstance of shunt it is equal to the combined resistance of winding 8, shunt i9 and reactor 2i. The influence of winding 43 and spring it? on the operation of the regulator is then negligible compared to that of windings i'i, M. The flow of current through windings M, 85 causes dis placement of sector 36 until the magneto-motive forces of the two windings become substantially equal and neutralize each other. The result is that the regulator tends to maintain the current through the converter equal to the current flowing through the generator. The regulator there= fore inherently imparts to the converter the steady state characteristic of the generator. During transient operation the characteristic of. the generator is modified in the same manner as in the embodiment illustrated in Fig. 1. The adjustment of the system may also be modified as above set forth with respect to the embodiment illustrated in Fig. 1.

In the embodiment illustrated in Fig. 4 the converter is assumed always to operate with generator t. windings 48 and 8d and spring 42 of regulator 31 are omitted and shunt i9 and reactor are connected across winding 8 through shunt 4t. Winding 41 then has the same effect as windings 4i and 84 in the embodiment illustrated in Fig. 3 and the regulator tends to impart to the converter the characteristic of genduring steady state operation. During transient operation the characteristic of the generator is above set forth with respect to the embodiments illustrated in Figs. 1 and 3.

Although but a few embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit o! the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. The combination of an alternating current circuit, a direct current circuit, a dynamoelectric machine comprising an armature wind- .ing and a field winding serially connected across said direct current circuit, and a current converting system comprising an electric valve for the conversion of current between said circuits, said system having connections with said alternating current circuit and being eifectively con-. nected in parallel with said armature winding and in series with said field winding, the connection of said field winding to said armature and said converting system providing for excitation of said field winding in response to the joint current of said armature winding and said converting system.

2. The combination of an alternatingcurrent circuit, a direct current circuit, a dynamoelectric machine comprising an armature winding and a field winding serially connected across said direct current circuit, a current converting system comprising an electric 'valve for the conversion of current between said circuits, said system having connections with said alternating current circuit and being eiiectively connected in parallel with said armature winding and in series with said field winding. the connection of said field winding to said armature and said converting system providing for excitation of said field winding in response to the Joint current of said armature winding and said converting system, and means responsive to the flow of current through said valve for controlling the conductivity of said valve.

3. The combination of an alternating current circuit, a'direct current circuit, a dynamoelectric machine comprising an armature winding and a field winding serially connected across said direct current circuit, a current converting system comprising an electric valve for the conversion of current between said circuits, said system having connections with said alternating current circuit and being effectively connected in parallel with said armature winding and in series with said field winding, the connection or said field winding to said armature and said converting system providing for excitation of said field winding in response to'the joint current of said armature winding and said converting system, and a shunt connected in parallel with said field winding.

4. The combination of an alternating current circuit, a direct current circuit, a dynamoelectric machine comprising an armature winding and a field winding serially connected across said direct current circuit, a current converting system comprising an electric valve for the conversion of current between said circuits, said system having connections with said alternating current circuit and being effectively connected in parallel with said armature winding and in series with said field winding, the connection or said' field winding to said armature and said converting system providing for excitation of 'said'field winding in response to the Joint current ot-said armature winding and said converting system, and a shunt connected in parallel with said field winding and having a ratio of inductance to resistance substantially equal to that of said field winding.

5. The combination of an alternating current circuit. a direct current circuit, a dynamoelectric machine comprising an armature winding and a field winding serially connected across said direct current circuit, a current converting system comprising an electric valve for the conversion ofcurrent between said circuits, said system having connections with said alternating current circuit and being effectively connected in parallel with said armature winding and in series with said field winding, the connection of said field winding to said armature and said converting system providing for excitation 01' said field winding in response to the joint current of said armature winding and said converting system, means responsive to the flow of current through said valve for controlling the conductivity of said valve, and a shunt connected in parallel with said field winding.

6. The combination of an alternating current circuit, a direct current circuit, a dynamoelectric machine'comprising an armature winding and a field winding serially connected across said direct current circuit, a current converting system comprising an electric valve for the conversion of current between said circuits, said system having connections with said alternating current circuit and being effectively connected in parallel with said armature winding and in series with said field winding, the connection of said field winding to said armature and said converting system providing for excitation of said field winding in response to the Joint current of said armature winding and said converting system, and means responsive to the fiow of current through said valve and to the fiow of current through said machine for controlling the conductivity of said valve.

7. The combination of an alternating current circuit, a direct current circuit, a dynamoelectric machine comprising an armature winding and a field winding serially connected across said direct current circuit, a current converting system comprising an electric valve for the conversion of current between said circuits, said system having connections with said alternating current circuit and being efiectively connected in parallel with said armature winding and in series with said field winding, the connection of saidfield winding to said armature and said converting system providing for excitation of said field winding in response to the joint current of said armature winding and said converting system. and means responsive to the voltage of said direct current circuit, the fiow of current through said valve and the fiow of current through said machine for controlling the conductivity of said valve.

8. The combination of an alternating current circuit, a direct current circuit, a dynamoelectric machine comprising an armature winding and a field winding serially connected across said direct current circuit, a current converting system comprising an electric valve for the conversion of current between said circuits, said system having connections with said alternating current circuit and being eiiectively connected in parallel with said armature winding and in series with said field winding, the connection of said iield winding to said armature and said converting system providing for excitation of said field winding in response to the Joint current or said armature winding and said converting system, a shunt connected in parallel with said field winding, and means differentially responsive to the magnitudes of the currents in said series winding and in said shunt for controlling the conductivity of said valve.

9. The combination of an alternating current circuit, a direct current circuit, a dynamoelectrio machine comprising an armature winding and a field winding serially connected across said direct current circuit, a current converting system comprising an electric valve for the conversion of current between said circuits, said system having connections with said alternating current circuit and being effectively connected in parallel with said armature winding and in series with said field winding, the connection of said field winding to said armature and said converting system providing for excitation of said field winding in response to the Joint current of said armature winding and said converting system, a shunt connected in parallel with said series winding, regulating means for controlling the conductivity of said valve operable with a sub stantial time of response in dependence upon variations in the now oi current between said circuits, and inductive means in said shunt for controlling the current distribution between said converting system and said dynamoelectrlc machine during the time of response of said regulating means.

JAMES G. LINN. 

